why hassle with the old one? A new water heater is cheap and the peace of mind is priceless. I put in a new Atwood, it took about 20 minutes. I chose the pilot light model, for I am always checking anyhow, and felt it was no big deal to light. I however, also like to crank my jack stand manually. If you save all your Bowen cover parts you can make a false door for your new one like this.

I do not think saving the original will effect your value if that is your concern. All that sediment cannot be good for you or the operation of the unit.